Method for deeply degrading TOC (Total Organic Carbon) in rare earth wastewater based on catalytic ozonation technology

Abstract

The invention discloses a rare earth wastewater TOC deep degradation method based on a catalytic ozonation technology, and particularly relates to the technical field of rare earth chemical wastewater treatment. The method comprises the steps of pretreatment, primary filtration, catalytic oxidation, carbonization, secondary filtration, drying and saponification. The rare earth wastewater TOC deep degradation method based on the catalytic ozonation technology solves the problem that residual organic matter (extractant) in rare earth wastewater is difficult to degrade; the TOC concentration can be reduced to be less than 40 mg / L after the treatment by using the method disclosed by the invention; according to the method, rare earth elements can be fully recycled; according to the method disclosed by the invention, calcium carbonate and magnesium hydroxide are recycled, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth chemical wastewater treatment, and particularly relates to a method for deeply degrading TOC of rare earth wastewater based on ozone catalytic oxidation technology. Background Art

[0002] There are many varieties of rare earth minerals in China. A large amount of saponification wastewater and raffinate are generated during the smelting, separation and extraction processes. Usually, traditional oil separation tanks + activated carbon adsorption and oil separation tanks + air flotation processes are used to remove oil, and then evaporation crystallization is carried out. However, due to incomplete oil removal, and the wastewater contains high concentrations of calcium, magnesium and sodium, as well as a small amount of residual rare earth ions, it increases the treatment difficulty of the evaporation crystallization mother liquor, affects the product purity, and the recovered calcium and magnesium are also difficult to reuse, resulting in waste of resources.

[0003] The oil in rare earth wastewater is mainly acidic extractants (such as P 507 、P 204 、C 272 etc.). In view of the characteristics of these extractants, researchers have developed a variety of specific adsorption oil removal materials. For example, Chinese Patent CN 103805781 B discloses a method for extracting organic extractants in wastewater using insoluble rare earth compounds as adsorbents. This method utilizes the weak basicity of various rare earth compounds to react with acidic extractants to generate insoluble rare earth organic saponification materials to achieve the effect of reducing COD. However, the recovery of the organic phase requires acid soaking, which will cause the dissolution of rare earth compounds and is not suitable for treating wastewater with a high oil concentration. The specific adsorption material disclosed in Patent CN 106946379 A can reduce the oil content to less than 1 mg / L, but the adsorption capacity of the adsorption material for some small molecule organic substances generated by the chain breaking of extractants is limited, and the COD concentration in the effluent will exceed the standard after long-term use.

[0004] Regarding the high concentrations of calcium and magnesium ions in the wastewater, Patent CN 106946379 A discloses a method for recovering hydrochloric acid by using an acid retardation resin and then evaporating and crystallizing to recover calcium chloride with a higher purity. However, the recovered acid concentration is low, and the rare earth wastewater also contains a large amount of sodium ions, and the purity of the crystalline miscellaneous salts is low and difficult to be recycled. Patent CN 116730557 A discloses a method for removing calcium with oxalic acid and then removing magnesium with sodium hydroxide combined with PAM. By this method, calcium oxalate and magnesium hydroxide can be recovered step by step, but the dosage of oxalic acid is not easy to control and easily causes an increase in the TOC concentration of the wastewater. Patent CN 219991377U discloses a carbon dioxide hardness removal system. First, sodium hydroxide is used to adjust the pH to remove magnesium, and then carbon dioxide is introduced to remove calcium. After treatment, the hardness of the wastewater is below 40 mg / L. However, this method has poor removal efficiency for calcium and magnesium in organic complexes, especially when there are residual extractants in rare earth wastewater, organic complexes of calcium and magnesium ions will be formed. Summary of the Invention

[0005] To this end, the present invention provides a method for deep degradation of TOC in rare earth wastewater based on ozone catalytic oxidation technology to solve the above-mentioned problems.

[0006] The present invention solves the problem of difficult degradation of organic matter in high-chloride and high-salt rare earth wastewater through catalytic ozone oxidation technology. At the same time, it fully utilizes the CO2 generated by the organic matter mineralization and saponification process to convert calcium ions and magnesium ions in the wastewater into CaCO3 and Mg(OH)2, which are reused in the saponification process, thereby realizing the recycling of CaCO3 and Mg(OH)2 in the entire process flow and effectively reducing wastewater treatment costs and production costs.

[0007] Based on the water quality characteristics of rare earth wastewater, the present invention proposes a rare earth wastewater TOC deep degradation method based on ozone catalytic oxidation technology, which efficiently degrades TOC while recycling high-concentration calcium and magnesium ions in the wastewater, reducing wastewater treatment costs.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] According to the present invention, a method for deep degradation of TOC in rare earth wastewater based on ozone catalytic oxidation technology is provided, the method comprising:

[0010] Step 1, pretreatment: adding alkaline reagent to the wastewater while stirring, so that the rare earth ions and part of the magnesium ions in the wastewater are converted into basic rare earth and Mg(OH)2 precipitation;

[0011] Step 2, first filtration: the pre-treated wastewater is filtered through a filtration device for solid-liquid separation, the filtrate enters a catalytic oxidation tower, and the filter cake enters the subsequent step 6 for drying;

[0012] Step 3, catalytic oxidation: degrade the TOC in the filtrate of step 2 by catalytic oxidation with ozone, and part of the Ca 2+ and Mg 2 + ;

[0013] Step 4, carbonization: After the effluent from catalytic oxidation enters the carbonization tower, CO2 and the carbon dioxide produced by the saponification reaction in step 7 are introduced to remove calcium and magnesium ions;

[0014] Carbon dioxide removal of calcium 2+ Mg 2+ The principle is as follows:

[0015] ;

[0016] ;

[0017] ;

[0018] Step 5, secondary filtration: Separate the solid and liquid of the effluent from the carbonation tower. The solid phase enters the oven for drying and then is recycled, and the filtrate enters the subsequent treatment process for desalination treatment;

[0019] Step 6, drying: Dry the solid precipitate obtained in Step 2 and Step 5 through a drying device;

[0020] Step 7, saponification: Crush the solid product recovered by the drying unit and use it for the saponification process. The by-product carbon dioxide is introduced into the carbonation tower to remove calcium and magnesium ions;

[0021] Further, in Step 1, control the stirring speed at 100 - 600 rpm and the stirring time at 10 - 20 min to fully mix the wastewater with the alkaline reagent, and then let it stand for 20 - 30 min; the alkaline reagent is one or several of sodium hydroxide, potassium hydroxide, and lime milk, and the addition amount is to adjust the pH of the wastewater to 9.5 - 12.5;

[0022] Further, in Step 2, the filtering equipment adopts a chamber filter press, a plate and frame filter press, a belt filter press, or a diaphragm squeeze filter press;

[0023] Further, in Step 3, the ozone supply method adopts a common aeration disk, dissolved air, or micro-nano bubble aeration; the catalytic material is a filler loaded with one or more transition metal oxides or H2O2; the mass ratio of ozone aeration volume to COD is 1.5:1 - 2:1; the transition metal oxides are selected from one or several of TiO2, Al2O3, NiO, MnO2, and Fe3O4; the carrier of the filler is selected from one or several of activated carbon, Al2O3, zeolite, molecular sieve, ceramic, diatomite, and graphene, and is filled in the catalytic reaction tower; the dosage of H2O2 in the oxidation is 2‰ - 5‰;

[0024] Further, in Step 4, the carbon dioxide comes from a CO2 cylinder and the saponification reaction; the carbon dioxide is introduced into the carbonation tower by a dissolved air device; the reaction time is 20 - 30 min; the optimal reaction pH is 9.5 - 12.5; the carbon dioxide flow rate is 0.15 - 0.3 L / min; the carbonation reaction takes the calcium removal rate reaching 99% as the reaction end point.

[0025] Further, in Step 5, the filtering equipment is selected from a chamber filter press, a plate and frame filter press, a belt filter press, or a diaphragm squeeze filter press;

[0026] Further, in Step 6, the drying temperature is 100 - 400 °C;

[0027] Further, in Step 7, the saponification reaction is carried out in a closed container with a stirring paddle; the carbon dioxide generated by the saponification reaction is introduced into the carbonation tower to remove calcium and magnesium ions.

[0028] The present invention has the following advantages:

[0029] The method for deeply degrading TOC of rare earth wastewater based on ozone catalytic oxidation technology of the present invention solves the problem of difficult degradation of residual organic matter (extraction agent) in rare earth wastewater; after treatment by the method of the present invention, the TOC concentration can be reduced to below 40 mg / L; the method of the present invention can fully recover rare earth elements; the method of the present invention realizes the cyclic recycling of calcium carbonate and magnesium hydroxide, reducing production costs.

[0030] The treatment process of the present invention hardly generates hazardous waste; the overall process of the degradation method of the present invention is simple and has good stability. Description of the Drawings

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can be obtained according to the provided drawings.

[0032] The structures, ratios, sizes, etc. depicted in this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have technical substance significance. Any modification of the structure, change in the ratio relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention.

[0033] Figure 1 It is a process flow diagram of a method for deeply degrading TOC of rare earth wastewater based on ozone catalytic oxidation technology provided in Embodiment 1 of the present invention;

[0034] Figure 2 It is an ozone catalytic oxidation reaction tower provided in Embodiment 2 of the present invention. In the figure, 1 is the inlet water pump pipe, 2 is the water distribution pipe, 3 is the ozone catalytic filler, 4 is the ozone aeration device, 5 is the water outlet, 6 is the sampling port distributed on the first tower wall, 7 is the sampling port distributed on the second tower wall, 8 is the sampling port distributed on the third tower wall, 9 is the maintenance port on the first tower body, 10 is the maintenance port on the second tower body, 11 is the maintenance port on the third tower body, and 12 is the ozone tail gas discharge port. Detailed Embodiments

[0035] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0036] Example 1

[0037] The pH of a certain rare earth wastewater is about 0, and the concentrations of rare earth elements Ce, La, and Nd are 0.745, 1.402, and 0.646 mg / L respectively, the concentrations of calcium and magnesium are 53800 and 294 mg / L respectively, and the TOC concentration is 360 mg / L.

[0038] According to the treatment method of this embodiment, the treatment process is as Figure 1 shown as follows:

[0039] Step 1: Adjust the pH of the rare earth wastewater to 10.0 with NaOH and let it stand for 20 min;

[0040] Step 2: Filter with a vacuum filter. Ce and Nd in the filtrate are basically completely removed, the La concentration is reduced to 0.310 mg / L, the magnesium ion concentration in the filtrate is reduced to 166 mg / L, and the TOC concentration is reduced to 230 mg / L;

[0041] Step 3: The filtrate of Step 2 undergoes an oxidation reaction in a catalytic oxidation tower. The aeration head is a titanium alloy aeration head with a pore size of 10 microns. After reacting for 30 min, the TOC concentration is reduced to 35 mg / L, the calcium ion concentration is reduced to 14269 mg / L, and the magnesium ions are basically completely removed;

[0042] Step 4: Introduce CO2 into the carbonization tower, and the calcium concentration is reduced to 364 mg / L;

[0043] Step 5: The solid precipitate obtained after filtering the reaction effluent in Step 4 is dried in an oven at 100 °C for 2 h and then reserved for use;

[0044] Step 6: Grind the solids obtained in Step 2 and Step 5, add water to make a suspension, mix and react with P507 in a closed container. After the reaction, let it stand and separate into layers. The upper organic phase is the saponified P507.

[0045] Example 2

[0046] The ozone catalytic oxidation reaction tower treated in Example 1 is as Figure 2As shown in the figure, the reaction tower includes a water inlet pump pipe 1, a water distribution pipe 2, an ozone catalytic filler 3, an ozone aeration device 4, a water outlet 5, a sampling port 6 distributed on the first tower wall, a sampling port 7 distributed on the second tower wall, a sampling port 8 distributed on the third tower wall, a maintenance port 9 on the first tower body, a maintenance port 10 on the second tower body, a maintenance port 11 on the third tower body, and an ozone tail gas discharge port 12.

[0047] The wastewater enters the water distribution pipe 2 through the water inlet pump pipe 1 and then reaches the ozone catalytic filler 3 for ozone catalysis. The ozone in the ozone aeration device 4 enters the ozone catalytic filler 3 for reaction, and the oxidized wastewater exits through the water outlet 5.

[0048] The sampling port 6 distributed on the first tower wall is located on one side of the water distribution pipe 2, the sampling port 7 distributed on the second tower wall is located on one side of the ozone catalytic filler 3, and the sampling port 8 distributed on the third tower wall is located on one side of the ozone aeration device 4, which are respectively used for sampling and detection.

[0049] The maintenance port 9 on the first tower body is distributed on the other side of the water distribution pipe 2, the maintenance port 10 on the second tower body is located on the other side of the ozone catalytic filler 3, and the maintenance port 11 on the third tower body is located on the other side of the ozone aeration device 4. The ozone tail gas is discharged through the ozone tail gas discharge port 12.

[0050] The carrier of the filler in the ozone catalytic filler 3 is selected from one or several of activated carbon, Al2O3, zeolite, molecular sieve, ceramic, diatomaceous earth, and graphene, and is filled in the catalytic reaction tower.

[0051] Example 3

[0052] A certain rare earth wastewater has a pH of about 0, and the calcium and magnesium concentrations are 20720 mg / L and 676 mg / L respectively, and the TOC is 735 mg / L.

[0053] According to the treatment method of this example, it is as follows:

[0054] Step 1: Adjust the pH of the rare earth wastewater to 11.5 with NaOH and let it stand for 20 min;

[0055] Step 2: Filter with a vacuum filter. The magnesium ion concentration in the filtrate is reduced to 7.2 mg / L, and the TOC concentration is reduced to 280 mg / L. The filtrate enters the catalytic oxidation reaction tower for further treatment, and the filter residue is collected for standby;

[0056] Step 3: The filtrate in Step 2 undergoes an oxidation reaction in the catalytic oxidation tower. The aeration head is a titanium alloy aeration head with a pore size of 10 microns. After 45 min of reaction, the TOC concentration is reduced to 32.4 mg / L, the calcium ion concentration is reduced to 427 mg / L, and the magnesium ions are basically completely removed;

[0057] Step 4: CO2 is introduced into the carbonation tower, and the calcium ion concentration is reduced to 273 mg / L;

[0058] Step 5: The solid precipitate obtained after filtering the water produced in the reaction in Step 4 is dried in an oven at 100 °C for 2 h and then reserved for use;

[0059] Step 6: The solids obtained in Step 2 and Step 5 are ground and then mixed with water to form a suspension, which is mixed and reacted with P507 in a closed container. After the reaction ends, it is left to stand for stratification, and the upper organic phase is the saponified P507.

[0060] Comparative Example 1

[0061] The difference from Example 3 is only that in Step 3, the catalytic oxidation tower is provided by ozone micro-nano bubbles. The results show that after only 20 min of reaction, the TOC concentration is reduced to 24.5 mg / L, and the calcium ion concentration is reduced to 406 mg / L.

[0062] Comparative Example 2

[0063] The difference from Example 3 is only that in Step 3, the catalytic oxidation tower is provided by a jet injector. The results show that after only 30 min of reaction, the TOC concentration is reduced to 25.3 mg / L, and the calcium ion concentration is reduced to 412 mg / L.

[0064] Comparative Example 3

[0065] The difference from Example 3 is only that 2‰ H2O2 is added as a catalyst in Step 3. The results show that after only 20 min of reaction, the TOC concentration is reduced to 20.6 mg / L, and the calcium ion concentration is reduced to 376 mg / L.

[0066] It can be seen from the comparative examples that compared with the titanium alloy aeration head, the two gas supply methods of ozone micro-nano bubbles and jet aeration have higher TOC degradation efficiency. This is because the solubility of ozone is higher in these two aeration methods and the utilization efficiency is high. In addition, the addition of an ozone catalyst can increase the conversion rate of ozone to hydroxyl radicals and expand the applicable pH range of the ozone catalytic oxidation reaction, which has an obvious promoting effect on the degradation of TOC.

[0067] Although the present invention has been described in detail above with general descriptions and specific embodiments, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A method for deep degradation of TOC in rare earth wastewater based on ozone catalytic oxidation technology, characterized in that, The method includes the following steps: Step 1, pretreatment: While stirring the wastewater, add an alkaline reagent to convert rare earth ions and some magnesium ions in the wastewater into basic rare earth and Mg(OH)₂ precipitates; Step 2, primary filtration: Subject the pretreated wastewater to solid-liquid separation through a filtration device. The filtrate enters the catalytic oxidation tower, and the filter cake enters Step 6 for drying treatment; Step 3, catalytic oxidation: Degrade the TOC in the filtrate from Step 2 through ozone catalytic oxidation, and part of Ca 2+ and Mg 2+ ; Step 4, carbonization: After the catalytic oxidation effluent enters the carbonization tower, introduce CO₂ and the carbon dioxide generated from the saponification reaction in Step 7 to remove calcium and magnesium ions; Step 5, secondary filtration: Conduct solid-liquid separation on the effluent from the carbonization tower. The solid phase is dried in an oven and then recovered, and the filtrate enters the subsequent treatment process for desalination treatment; Step 6, drying: Use a drying device to dry the solid precipitates obtained in Step 2 and Step 5; Step 7, saponification: Crush the solid product recovered from the drying unit and use it for the saponification process. The by-product carbon dioxide is introduced into the carbonization tower to remove calcium and magnesium ions.

2. The method for deeply degrading TOC of rare earth wastewater based on ozone catalytic oxidation technology according to claim 1, characterized in that, In Step 1, control the stirring speed at 100 - 600 rpm and the stirring time at 10 - 20 min to fully mix the wastewater with the alkaline reagent, and then let it stand for 20 - 30 min; the alkaline reagent is one or several of sodium hydroxide, potassium hydroxide, and lime milk, and the addition amount is adjusted to make the pH of the wastewater reach 9.5 - 12.

5.

3. A method for deep degradation of TOC in rare earth wastewater based on ozone catalytic oxidation technology according to claim 1, characterized in that, In Step 2, the filtration device is a chamber filter press, plate and frame filter press, belt filter press, or diaphragm squeeze filter press.

4. A method for deep degradation of TOC in rare earth wastewater based on ozone catalytic oxidation technology according to claim 1, characterized in that, In Step 3, the ozone supply method is ordinary aeration disk, jet, dissolved air, or micro-nano bubble aeration; the catalytic material is a filler loaded with one or more transition metal oxides or H₂O₂; the mass ratio of ozone aeration volume to COD is 1.5:1 - 2:1; the transition metal oxides are selected from one or several of TiO₂, Al₂O₃, NiO, MnO₂, and Fe₃O₄; the carrier of the filler is selected from one or several of activated carbon, Al₂O₃, zeolite, molecular sieve, ceramic, diatomaceous earth, and graphene, and is filled in the catalytic reaction tower; the dosage of H₂O₂ is 2‰ - 5‰.

5. A method for deeply degrading TOC of rare earth wastewater based on ozone catalytic oxidation technology according to claim 1, characterized in that, In Step 4, the carbon dioxide comes from a CO₂ cylinder and the saponification reaction; the carbon dioxide is introduced into the carbonization tower using a dissolved air device; the reaction time is 20 - 30 min; the reaction pH is 9.5 - 12.5; the carbon dioxide flow rate is 0.15 - 0.3 L / min; the carbonization reaction takes the calcium removal rate reaching 99% as the reaction end point.

6. A method for deep degradation of TOC in rare earth wastewater based on ozone catalytic oxidation technology according to claim 1, characterized in that, In Step 5, the filtration device is selected from a chamber filter press, plate and frame filter press, belt filter press, or diaphragm squeeze filter press.

7. A method for deep degradation of TOC in rare earth wastewater based on ozone catalytic oxidation technology according to claim 1, characterized in that, In Step 6, the drying temperature is 100 - 400°C.

8. A method for deep degradation of TOC in rare earth wastewater based on ozone catalytic oxidation technology according to claim 1, characterized in that, In Step 7, the saponification reaction is carried out in a closed container with a stirring paddle; the carbon dioxide generated from the saponification reaction is introduced into the carbonization tower to remove calcium and magnesium ions.

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